People with health problems are being warned to stay indoors today as air pollution reaches maximum levels.

Much of the south will be hit by smog as a result of toxic mix of pollution from Europe, dust from the Saharan desert and local emissions.

East Anglia was worst hit by the smog yesterday but today it will affect much of England and Wales.

One of Britain's top doctors, Dr Paul Cosford, of Public Health England, warned 'vulnerable people' to avoid strenuous exercise in the coming days.

Speaking on Radio 4's Today programme he said: "That most important advice is for those people who are vulnerable, if you're in a high pollution area, to reduce the amount of strenuous exercise outdoors over the next few days.

"Carry on life as normal – be aware you may need to use your inhalers more frequently – but carry on your life as normal.

"We do have problems with air pollution in our cities. The main sources we have are vehicle transport and the industrial process, when you put that alongside the unusual weather consequences like the Saharan dust... then that's when you get these few days of unusually high pollution."